1. Field of the Invention
The present invention relates to a refrigerant compressor having a protective iron sulfide layer for use with HFC 134a as a refrigerant.
2. Description of the Related Art
Refrigeration equipment is used for many domestic and commercial cooling applications. Commonly, such equipment takes the form of room air conditioners, automobile air conditioners, and refrigerators. At its most basic, refrigeration equipment includes a compressor, a refrigeration fluid, and a refrigeration oil. Known compressors include hermetic refrigerant compressors and automobile type semi-hermetic refrigerant compressor.
The compressors all have one or more moving parts which frictionally contact or slide against other parts inside the casing. For example, hermetic, rotary type refrigerant compressors have a motor mechanism and a compression mechanism which are disposed in an hermetic casing. The motor mechanism drives the compression mechanism through a connecting drive shaft.
The compression mechanism is a roller that is rotatably inside a cylinder and connected to the drive shaft off the rotational center of the roller. A blade extends through the cylinder and contacts the outer periphery of the roller so as to divide the inside of cylinder into an inlet chamber and an outlet chamber. By the resilient force of a spring, one end of the blade is maintained in constant frictional sliding contact with the outer periphery of the roller.
The roller orbits around the shaft as the shaft rotates thereby compressing the refrigerant. The compressed refrigerant is discharged into the casing and then via an outlet pipe on the casing to the refrigeration coils.
The primary friction surfaces in the refrigerant compressor are in the compression mechanism. For example, the blade rubs on the inner surface of the hole in the cylinder thereby causing wear on both the blade and the cylinder. In addition, the outer periphery of the spring forcing the blade against the roller also experiences frictional wear. The outer surface of the shaft and the inner surfaces of the frame and the bearing supporting the shaft are likewise subject to wear. Refrigerant oil dispersed in the refrigeration liquid is used to lubricate these surfaces to reduce the effects of friction. Accordingly, the chemical compatibility between the refrigerant and the refrigeration oil is important for achieving adequate lubrication of the friction surfaces. When the sliding parts become sufficiently worn, the performance of the refrigerant compressor is degraded to the point where the compressor must be retired from service. Particularly susceptible to frictional wear are the iron-containing materials commonly used for the compressor elements.
Common refrigerants for the aforementioned refrigerant compressors include dichloro-difluoromethane (hereinafter named CFC 12) and chloro-difluoromethane. Naphthene type mineral oil and paraffin type mineral oil are soluble in CFC 12 or chloro-difluoromethane and have been used as lubricating oils for the chlorofluorocarbon refrigeration systems.
Recent recognition that these chlorofluorocarbons adversely affects the atmospheric ozone have resulted in legislation that will mandate the elimination of chlorofluorocarbon refrigerants. Alternatives to chlorofluorocarbon refrigerants are now starting to be developed. They are not, however, without their drawbacks.
Two of the substitutes for CFC 12 are 1,1,1,2-tetrafluoroethane (hereinafter named HFC 134a) and 1,1-difluoroethane (hereinafter named HFC 152a). The HFC 134a is insoluble in the conventional chlorofluorocarbon refrigerator oils. As a result, polyether, polyester, and fluoride oils are used as lubricating agents. Unfortunately, these oils do not protect against frictional wear as well as the prior materials.
It is considered that wear on the sliding part takes place because the HFC134a and refrigerator oil are hygroscopic and pick up moisture as the compressor is operated. Because the refrigerant and refrigerator oil are directly circulated in the casing, the amount of absorbed moisture continues to increase while the sliding parts become increasingly more worn.
Another factor which contributes to wear inside the compressor is the chemistry of the refrigerant in relation to the iron-containing surfaces of the compressor. When CFC 12 is used as the refrigerant, chlorine atoms in CFC 12 react with iron atoms in the metal substrate throughout the compressor and form an iron chloride film which has high abrasion resistance. When HFC 134a is used, however, the absence of chlorine atoms does not allow the iron chloride layer to form. Compressors with HFC 134a wear faster than when CFC 12 is used.
If deliberate attempts are made to form an iron chloride layer on the compressor surfaces before the compressor is operated, the iron chloride layer is decomposed by water in the refrigerant. The decomposition products include hydrochloric acid which corrodes the compressor surfaces and exacerbates the wear rather than mitigating it. As a result, there exists a need for a method of forming a wear resistant coating on the iron-containing surfaces inside the compressor that is stable against adsorbed water.
Additionally, there is a need for a refrigerant compressor that uses HFC 134a as a refrigerant which has high wear resistance.